1. Field of the Invention
The present invention generally relates to dynamoelectric machines capable of operating in a generator mode or in a motor mode and, more specifically, to a compound interaction/induction dynamoelectric machine of the type having a distributed armature winding on a cylindrical rotor.
2. Description of the Prior Art
Most armatures have distributed windings i.e., windings which are spread over a number of slots around the periphery of a rotor or armature of the machine. In most conventional designs the machines are of a radial magnetic gap type so that electrical currents applied to the windings of the rotor or stator, or to the windings of both, generates electromagnetic fields in the rotor or in the stator, as the case may be. The torque or the EMF induced in the machine results from the interaction between the magnetic field in the radial magnetic gap and the generally parallel axial winding portions of the armature coils disposed in the axial grooves or slots of the armature. However, the back and front connections which are those portions of the windings which connect substantially diametrically opposing axial wire portions situated in the grooves have not been utilized in order to enhance the efficiency of the machine. Such front and back connections, which are substantially normal to the axis of the machine, rotate with the armature but have not been used to increase the torque of the machine, in the case of a motor, or to increase the power output, in the case of a generator. Specially designed special purpose dynamoelectric machines have been proposed in order to increase the efficiency and power output for given weight and size of the machine. One approach has been to use axial air gap type machines such as the brushless axial air gap inductor-type dynamoelectric machine disclosed in U.S. Pat. No. 3,467,844. The machine disclosed in the aforementioned patent uses plural variable reluctance rotors and a toroidal coil stator therebetween. However, the machine does not make use of a radial air gap. Accordingly, the machine requires a special construction which does not make use of conventional distributed armature-type windings.
In an effort to provide electric machines which are inexpensive and small in size, there has also been developed disc-type rotors in machines defining axial air gaps. One example of such a machine is disclosed in U.S. Pat. No. 3,558,947. In that patent, a D.C. motor is described which includes a disc armature and a permanent magnet stator providing an axial air gap. Such machines, which use axial air gaps and generally flat armatures are sometimes referred to as having a pancake coil. Such pancake coils or rotors contain all of the armature turns in a generally flat plane which is normal to the shaft or axis of the machine. There is, accordingly, no axial air gap as there is in conventional cylindrical rotor distributed armature winding machines. In some instances, instead of making use of a winding on a pancake-type rotor, a flat substrate is provided on which various winding patterns are printed. Such winding patterns may be etched, plated, printed or pressure bonded on such thin disc armature of insulating material. However, because of the difficulties which have been experienced with such thin disc-armatures, primarily because of the flexibility of the discs on which the conductors are placed, an electric machine has been disclosed in U.S. Pat. No. 3,487,246 which applies such conductive pattern on a conical surface of an insulating member. The purpose of making the armature conical is to provide a more rigid structure than the flat disc armature structures. Such flat substrate armature machines, however, whether flat or conical, cannot provide the mechanical or electrical power output as is possible with conventional cylindrical rotor machines.
U.S. Pat. No. 4,143,288 discloses a coreless motor which includes a rotor having a plurality of coils constituting a pancake coil. The motor disclosed in this patent is a special purpose motor which is capable of being attached to electrical parts such as balance weights, servo-mechanisms, etc. However, this motor likewise lacks the conventional cylindrical rotor found in most dynamoelectric machines which is provided with a distributed armature winding. As with the other pancake-type armatures, the coreless motor disclosed in this patent does not have a radial air gap and, therefore, does not have the ability to compound the interaction or induction in the machine both at the axial ends and the peripheral surface of the armature.
There has also been proposed a dynamoelectric machine which has plural stators. Such machines have been disclosed in U.S. Pat. Nos. 3,396,296; 3,426,224; 3,602,749; 3,729,642 and 4,114,057. These patents, all issued to the same patentee, were intended to combine advantages of using both the radial gap and axial gap in dynamoelectric machines. However, to do so, applicant disclosed a complicated structure making use of both inner and outer stators and a hollow cylindrical rotor. In these structures, a first stator is disclosed within the hollow cylindrical rotor and a second stator, also cylindrical in shape, is disposed such as to surround the rotor. In this way, double radial air gaps are formed. It was also suggested that end stators be used to form axial air gaps between the ends of the rotor and the magnetic field created by the end stators. These machines were described as having greater efficiency than conventional motors or generators as the result of the increased interaction between the multitude of magnetic field and electromagnetic fields. However, the machines proposed in the last mentioned series of patents are unconventional in design and construction, do not have radial grooves and do not have front and back armature winding connections at the axial ends of the rotor as is present in the normal distributed armature winding arrangements. Instead, the windings are each wound around a flat, relatively thin magnetic core.
Other special purpose dynamoelectric machines have been proposed for special applications. Thus, for example, in U.S. Pat. No. 4,051,401, a spherical air gap motor is disclosed wherein the magnetic ring closing the stator magnetic loop has a non-cynlidrical shape. Such electric motors with spherical air gaps have found applications in pump drives, particularly for hermetically sealed chemical pumps.
The prior art has not, however, heretofore utilized both radial and axial air gaps in cylindrical rotor machines having distributed armature windings. By harnessing the additional torque, in the case of motor operation, or the additional electromagnetic force, in the case of generator operation, significant improvements in efficiency can be obtained without compromising any constructional features and without the need to resort to unconventional, complicated or costly machine designs.